improving aluminum casting alloy and process competitiveness · improving aluminum casting alloy...

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Improving Aluminum Casting Alloy and Process Competitiveness

A. Mandal and Makhlouf M. Makhlouf

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Project Objectives

The objective of this project is to obtain a new family of

aluminum-silicon alloys that can be processed by high-

pressure die-casting at significantly lower than usual

temperatures and therefore is cost-effective; and that is heat-

treatable, and therefore is capable of significantly higher

ductility, with no sacrifice in other mechanical properties.

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Strategy

Phase 1 Developing a new family of aluminum-silicon alloys that is castable at significantly lower than usual temperatures.

Development of an optimum heat treatment schedule for the new alloy system.

Phase 2 Die-casting of the alloy system developed in Phase 1 at sufficiently low temperatures which will cause negligible soldering of the alloy to the die.

Phase 3 Exploring the possibility of heat-treating die cast samples.

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Background

Effect of Mg on Al-10Si alloy

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Effect of Mg on Al-14Si alloy

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Variation of Eutectic point

0 1 2 3 412.6

12.8

13.0

13.2

13.4

13.6

560

564

568

572

576

wt% Mg

Eute

ctic

Si,

wt.%

Eute

ctic

Tem

pera

ture

, o C

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Effect of cooling rate – Cast Iron Mold(220oC/min)

3 wt% Mg2 wt% MgAl-14Si alloy

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Effect of cooling rate – Copper Mold(300oC/min)

3 wt% Mg2 wt% MgAl-14Si alloy

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Average Size of Mg2Si

2.0 2.5 3.00

20406080

100120140160180200

Size

of M

g 2Si, µ

m

w t% Mg

Sand Cast (45oC/min) Cast Iron Mold (220oC/min) Copper Mold (300oC/min)

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Modifiers used for the modification of Mg2Si particles

0.2, 0.5, 1 wt%Calcium

0.02, 0.05, 0.2, 0.5 wt%Phosphorus

0.025, 0.050, 0.5, 1 wt%Strontium

0.25, 0.50, 0.75, 1 wt% Cerium

0.25, 0.50, 0.75, 1 wt%Yttrium

Addition level

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Effect of Yttrium

1 wt%0.75 wt%0.5 wt%

0.50 0.75 1.00160

165

170

175

180

185

Part

icle

siz

e of

Mg 2S

i, µm

wt% Y

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Effect of Cerium0.25 wt% 0.50 wt%

0.75 wt% 1.00 wt%

Mg2Si

Si

13

0.00 0.25 0.50 0.75 1.0020

40

60

80

100

120

140

160

180Pa

rtic

le s

ize

of M

g 2Si, µ

m

wt% Ce

Average size of Mg2Si

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Effect of Strontium0.050 wt%

0.50 wt% 1.00 wt%

0.025 wt%

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Modified morphology of Mg2Si

0.0 0.5 1.045

50

55

60

65

70

Part

icle

siz

e of

Mg 2S

i, µm

wt% Sr

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0.25 Ce + 0.050 Sr0.25 Ce + 0.025 Sr

Combined Effect of Ce and Sr

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SEM MicrographWith additionWithout addition

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Al-14Si-3Mg treated with0.25Ce + 0.025Sr

T6 – 4 hT4 – 1 dayas cast

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Mg2Si

Mg2Si

Eutectic Si

SEM Microstructures

T6 – 4 hT4 – 1 dayas cast

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300.51.041.143.8After 8 h

305.90.942.845.5After 4 hT6

367.34.426.039.2After 10 days

331.04.024.435.0After 1 dayT4

273.42.719.430.4-As cast

QI*(MPa)

%ElYS(ksi)

UTS(ksi)

0.25Ce + 0.025SrHeat TreatmentCondition#

Temper

Tensile Properties

* QI Ξ Quality Index = UTS (MPa) + 150 log [% El.]# Solution Treatment: 520oC for 12 h

Ageing Temperature: 200oC for 4 h & 8 h

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Effect of Phosphorus0.05 wt%

0.20 wt% 0.50 wt%

0.02 wt%

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0.1 0.2 0.3 0.4 0.580

100

120

140

160Pa

rtic

le s

ize

of M

g 2Si, µ

m

wt% P

Average size of Mg2Si

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Ca rich phase

Effect of Calcium

1 wt%0.5 wt%0.2 wt%

0 .2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0

6 0

8 0

1 0 0

1 2 0

1 4 0

1 6 0

Part

icle

siz

e of

Mg 2Si

, µm

w t% C a

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293.90.744.746.0After 8 h

276.30.840.542.2After 4 hT6

After 10 days

318.62.526.537.5After 1 dayT4

194.21.120.526.9-As cast

QI*(MPa)

%El.YS(ksi)

UTS(ksi)

0.5 wt% CaHeat TreatmentCondition#

Temper

Tensile Properties

* QI Ξ Quality Index = UTS (MPa) + 150 log [% El.]# Solution Treatment: 520oC for 12 h

Ageing Temperature: 200oC for 4 h & 8 h

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Isopleths of Al-14Si-3Mg-xCu alloys

Θ = Al2Cu

Q = Al5Cu2Mg8Si6

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% Phases inAl-14Si-3Mg-xCu alloys

0 1 2 3 4 5 60123456789

1 0

a t e le v a te d te m p e ra tu re

A l2C u

M g 2S i

M g 2S i

A l5C u 2M g 8S i6

Con

stitu

ent (

wt.%

)

C u (w t.% )

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As Cast Microstructure – Sand mold(45oC/min)

Q phaseSi

Al2Cu

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Effect of Solutionising Times at 480oC

36 h24 h12 h

Q phase Q phase

Q phase

fragmentationspheroidisationno change

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As cast ST = 12 h ST = 24 h ST = 36 h

8

10

12

14

16

18

Size

of Q

pha

se, µ

m

Heat Treatment Condition

Average size of Q phase

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Summary

Hypereutectic Al-14Si-3Mg-0.2Fe alloys with Yttrium, Cerium, Strontium, Phosphorus and Calcium addition was tried out with a view to modify the Mg2Si particles. One of the alloys showed an elongation of 4.4% (T4 condition) and a tensile strength of 46 ksi (T6 condition).

The scope of Cu addition to Al-14Si-3Mg alloy was assessed and results indicated that spheroidisation of Q phase was possible for higher solutionising times.

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Deadlines for the Project

December 2008Phase III

June 2008Phase II

December 2007Phase I

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